The broad, long-term objective of the proposed research is the laboratory demonstration and clinical introduction of a noninvasive ophthalmologic imaging technology to characterize changes in the neurotubules of retinal ganglion cell (RGC) axons associated with the onset and progression of glaucoma. Although numerous damage mechanisms and apoptotic signaling pathways are under investigation in glaucoma research, the pathologic hallmark for glaucoma in human eyes is selective death of RGCs and accompanying degeneration of axonal neurotubules within the retinal nerve fiber layer (RNFL). Enhanced polarization-sensitive optical coherence tomography (EPS-OCT) combines the high resolution cross-sectional imaging capability of optical coherence tomography (OCT) with the polarimetric-sensitivity of scanning laser polarimetry (SLP) to simultaneously measure RNFL thickness (ZRNFL), retardation (?RNFL) and birefringence (?nRNFL) with high sensitivity and accuracy. Because RNFL birefringence (?RNFL) is directly related to the density of neurotubules in RGC axons, the principal investigator and colleagues believe research studies proposed herein will establish that EPS-OCT can objectively and noninvasively monitor RGC neurotubule density (?RGC) and therefore has significant advantages in sensitivity and specificity over existing methods for diagnosis and monitoring of glaucoma. The specific aims of this application are to: 1. Construct a fiber-based spectral domain EPS-OCT instrument for measuring RNFL birefringence (?RNFL) and verify that the instrument has sensitivity and accuracy necessary for noninvasive quantification of RGC neurotubule density (?RGC) in the RNFL. 2. Experimentally validate the mathematical relationship between RNFL birefringence (?RNFL) and RGC neurotubule density (?RGC) using the fiber-based spectral domain EPS-OCT instrument and transmission electron microscope (TEM) histology. 3. Characterize the temporal and spatial dynamics of RNFL birefringence (?RNFL) and RGC neurotubule density (?RGC) during the progression from healthy to advanced glaucoma in experimental rat and primate glaucoma models. 4. Using ROC analysis, formulate and test a feature set and classifier based on RNFL thickness (ZRNFL), retardation (?RNFL), and birefringence (?RNFL) for discriminating between normal and glaucomatous human eyes. [unreadable] [unreadable]